iOS 6 and earlier users can upgrade over-the-air by navigating to "Software Update" in the "General" section of the device's settings. Thee update is large so you'd better connect via a Wi-Fi connection.

Alternatively, Windows and Mac users can connect their compatible iPhones, iPads, and iPod touches to the latest version of iTunes 11.1 and upgrade by selecting the "Check for Upgrade" button in their device's summary window.